Generally, street lamps are lighting facilities constructed along a street for traffic safety and security on the road, and a suitable type of street lamp is used depending on the places where the street lamps are installed, such as a highway, a main street in a city, a road in a commercial district, a road in a residential area, and the like.
The lighting apparatus includes a lamp housing provided with a reflecting plate on the inner side surface and installed on a street lamp pole, and a light source mounted inside the lamp housing and emitting light. There are various types of street lamp poles, such as a highway type in which the top portion of a pole is bent and a lamp is attached at the end point, a bracket type in which branches are extended from the top of a pole and a lamp is attached at the end of each branch, and a pole-head type in which a lamp is attached on the top of a pole.
In addition, a high pressure mercury lamp, a fluorescent lamp, a natrium lamp, a general electric lamp, or the like is used as the light source. The street lamp emits white, yellow, or blue light by the light source of a predetermined color. It is apparent that the street lamp can be selected based on efficiency of power, intensity of light, or atmosphere of surrounding areas.
On the other hand, when the street lamps are installed on the road, light distribution for distributing light on the road is designed to illuminate the road most efficiently, and when bulb-type lamps are used, illumination of the road is designed to illuminate the road with proper light distribution by adjusting a reflecting angle of the reflecting plate provided on the inner side surface the lamp housing.
Generally, as shown in FIG. 10, light distribution mainly used for illuminating a road is divided into first to fifth light distribution types, and except some special cases, the second to fourth light distribution types are mainly used to efficiently illuminate most of the roads.
However, various types of lamps used as a light source in the conventional street lamps, such as a high pressure mercury lamp, a fluorescent lamp, a natrium lamp, and the like, are disadvantageous in that light intensity and diffusing range are predetermined when the lamps are initially manufactured and cannot be manually adjusted by a user. Furthermore, the lamps have a very short lifespan and consume a large amount of power.
Considering these problems, lighting apparatuses using light-emitting diodes (LED) as a light source are proposed recently. With the advancement of technologies, LEDs consuming a small amount of power and emitting light of high brightness are developed, and use of the LEDs tends to be gradually increased. Since light emitted from the high brightness LED has a high directionality, a lens unit (not shown) for scattering light emitted from the LED chip and classifying an irradiating range into a 12° lens, a 25° lens, a 30° lens, a 45° lens or the like is included when the LED chip is packaged in order to irradiate the high directional light on a wide area.
However, since the lighting apparatus using LEDs has a relatively small radiation angle compared with a bulb-type light source having a radiation angle of 360 degrees, it is general that a plurality of LED modules is mounted on the bottom surface of an upper plate unit of the housing and the lighting apparatus illuminates a road using the reflecting plate provided inside the side surface of the housing.
The lighting apparatus includes a plurality of LED modules on the bottom surface of the upper plate unit in order to secure a cut-off-angle so that a passenger or a driver cannot directly see the LED modules within a certain angle.
However, since street lamps using the high brightness LEDs may hinder walking or driving and cause safety accidents if a pedestrian or a driver directly sees the light emitted from the light source while walking or driving, securing the cut-off-angle is necessarily needed.
However, although the LED has a long lifespan as long as to say semi-permanent compared with conventional lamps, brightness of the LED is determined by combination of a plurality of LEDs. Therefore, if light distribution is formed using the reflecting plate, a light distribution area is small, and brightness of the light is low. Furthermore, there is a limit in forming light distribution that can efficiently illuminate road surfaces, i.e., in forming light distribution of the first to fifth light distribution types. Accordingly, an ideal array is excluded when the lighting apparatus using LEDs is manufactured, and brightness is provided depending only on the reflecting plate, and thus the lighting apparatus is not widely used since illumination on the road is inefficient.
Furthermore, since it is difficult to efficiently dissipate the heat emitted from the plurality of LEDs, light emitting efficiency is lowered due to the heat, and components of the lighting apparatus can be easily damaged.
In addition, conventional street lamps using LEDS or general street lamps use a transparent protection cover in order to protect lamps installed inside the housing. However, since the protection cover is mainly formed as a concave type protruding toward outside of the housing, a street lamp is formed in a shape protruding upward and downward, and overall volume of the lamp increases when the housing is coupled with the protection cover, and thus it is inconvenient to store and carry the lamp.
Furthermore, fixing pieces are used to mount the LED modules inside the housing, and connection holes are formed inside the housing at this point in order to attach the fixing pieces to the housing. However, a portion of the housing where the connection holes are formed should be thicker than the other portions of the housing, and thus weight of the housing increases. Accordingly, workers should make a lot of efforts with a great force when installing the street lamp on the pole, and thus it is difficult to install the street lamp. In addition, since the surface area of cooling fins formed on the thick portion of the housing is relatively smaller than that of the cooling fins formed on the thin portions, overall cooling efficiency is lowered.
Furthermore, if rainfalls infiltrate into the housing due to a poor waterproof structure between the housing and the protection cover, a lamp installed inside the housing or electronic elements installed on a printed circuit board are affected by the rainfalls, which causes malfunctions of the street lamps.